Memory that retains its data even when operation power is not available is classified as nonvolatile memory. Examples of non-volatile memory are nvSRAM, F-RAM, electrically erasable programmable read-only memory (EEPROM), and flash memories. This class of memory may be used in applications in which critical data must be stored after power is removed, or when power is interrupted during operation.
Reference voltage for a memory device or cell may be interpreted as a voltage level that separates what is to be considered a data value “0” or a “1” stored, depending on the charge stored/generated in the memory device or cell. In certain embodiments, voltages found on the memory bus below the reference voltage are to be considered a “0” and voltages above the reference voltage are to be considered a “1”, or vice versa. Depending on the system requirements or design preferences, the reference voltage may be kept at a constant level, programmable, or a combination thereof. In some embodiments, no reference voltage/signal will be used. Instead, complementary memory cells (true bit and complementary bit) will be compared to one another to determine the binary state of the true memory cell.
To achieve an accurate and reliable read, it is important to maintain sensing devices, such as sense amplifiers, to be as balanced and symmetrical as possible during the read operation.